HIGH BANDWIDTH MICROSTRIP ANTENNA OF ELLIPTICAL PATCH WITH SQUARE SLOT AND A PIN SHOT

HIGH BANDWIDTH MICROSTRIP ANTENNA OF ELLIPTICAL PATCH

WITH SQUARE SLOT AND A PIN SHOT

Mahendra Singh Meena

Assistant Professor, Department of Electronics and Communication Engineering, Amity School of Engineering and Technology, Amity University, Haryana.

ABSTRACT

FR4 is an inexpensive and easily available substrate material, which can be used to design

efficient and cost effective microstrip patch antenna. This paper focuses on increasing the

bandwidth of the microstrip patch antenna. Paper discusses about design of a elliptical patch

antenna, having coaxial probe as a feed. To get the improved bandwidth, a rectangular slot has

been digged along with a pin short, which changes the interaction of radiation. A huge increase

in bandwidth is observed using the proposed design; almost 9 fold. All the simulation work is

done using IE3D simulating software from Zeland has been used.

Key words: FR4, elliptical, slot, pin short

Introduction

A Microstrip or Patch Antenna is a low profile Antenna that has a number of advantages over other antennas. It is lightweight, inexpensive, and easy to integrate with accompanying electronics. While the antenna can be 3D in structure (wrapped around an object, for example), the elements are usually flat, hence their other name, Planar Antennas. A Planar Antenna is not always a patch antenna. But use of conventional elliptical microstrip patch antenna alone is very difficult because of its low gain and narrow bandwidth. So to overcome these problems various methods have been tried, some of them are listed in next section. This paper proposes a method in which slots are digged in patch antenna using pin short. Configuration of paper is as follows:

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Next section is literature review, which is followed by proposed design and in the last some conclusions are drown based on simulation done.

Literature Review

The Gordon et.al described that the band width of microstrip antennas can be increased by using thick substrate but with thick substrate coaxial probe feed introduces inductive component due to which unavoidable impedance mismatch occurs. So the solution to impedance mismatch was found in the form of capacitive feeding mechanism which can be used for annular ring MPA elements, consisted a small capacitor patch in the same layer as in the radiating element. [1]

Gordon et.al experimented on following three designs:

• Rectangular radiating elements,

• Circular radiating elements and

• Annular ring radiating elements

Feeding mechanism was common in all three designs. The position of the probe feed was decided to be in the center of the small patch. Design tool used was IE3D 12th version Zeland, substrate was FR4 with thickness 1.6 mm having dielectric constant 4.4. Height of patch from ground was taken as 15 mm, ground plane was taken as square of 150x150 mm and probe diameter 0.9 mm.

Experimental Results are shown below:

Resonant frequency- 1800MHz

10 dB return loss Band Width-

Rectangular Circular Annular Ring Simulated 25.9% 26.8% 25.9% Measured 26.4% 27.9% 26.1% Gain-

Figure 1 Structure of proposed antenna design for (a) rectangular,(b) circular and (c) annular ring radiating elements (d) side view of anteena.

Dheeraj et. al. proposed modified circular patch antenna to achieve 50.36% efficiency together with 4.10 dBi gain and 8.38% band width. Firstly they taken a circular patch and then an elliptical slot has been cut in it, after this, parallel to major axis of the inserted elliptical slot, splitting is applied and at last this elliptical hole is filled with an elliptical patch between two split halves of circular patch.

FR4 of thickness 1.59 mm and dielectric constant 4.4 was taken as substrate which had loss tangent of 0.0148. Main circular patch radius was taken 12 mm. For inside elliptical patch semi major axis is of 9 mm, semi minor axis is of 4.8 mm and eccentricity is 0.846. Splitting width of circular patch in two halves is 0.25 mm. Ellipse filling the elliptical slot has a = 8 mm and b = 3 mm.

Experimental Results are shown below:

Geometries

Resonance frequency,

GHz

Radiation efficiency,

%

Directivity

, dBi Gain, dBi

Bandwidth , %

Circular elliptical ring 4.96 22.48 6.30 1.11 6.02 Gap coupled split

circular patch antenna with circular slot

5.16 53.35 7.61 4.87 6.64

Gap coupled split circular patch antenna with elliptical slot and filled with elliptical

patch

5.01 50.36 7.08 4.10 8.38

Figure 3: Design of proposed antenna

As a result resonating frequencies of 6.23GHz and 6.859GHz (simulating) and 6.66GHz and 7.42GHz (measured) were observed and bandwidth of 15.99% (simulated) and 13.58% (measured) along with Gain of 5.84 at 6.66GHz and 5.71 at 7.42GHz were observed, which is huge improvement over non-slotted design. [3]

To obtain improved bandwidth and circularly polarized radiation over conventional elliptical antenna, in this paper the elliptical shape patch antenna with truncated edges has been introduced. In [4] tow antennas were studied (1) a conventional elliptical antenna and (2) edges truncated elliptical antenna. FR4 with having thickness of 1.59 mm, dielectric constant of 4.4 and loss tangent of 0.025 was used as substrate. Ellipse patch with semi major axis a = 15 mm and semi minor axis b = 14.43 mm after truncation L1= L2=7.75 mm as shown in figure.

Figure 4 Edge truncated elliptical patch antenna

2.692 GHz and (48.49+ j5.34) ohm corresponding 2.802 GHz resonant frequency, Minimum Axial ratio = 0.68 dB at 2.751 GHz, Gain = 1.71 dB at 2.751 GHz

Proposed Design and Results Design Specifications:

In this design elliptical shape microstrip patch has been designed for broadband purposes by cutting a square shape slot and using a pin short. Design specifications of the patch are-

• Resonant Frequency f0 = 7.25GHz • Dielectric Constant ϵr = 4.4

• Substrate Thickness h = 1.59mm

• FR4 substrate is used

Dimension of the patch: Wireless communication requires compact size antenna, which can be easily used in small hand held devices. We have proposed a compact size elliptical shape patch, which can be utilized for the purpose. Dimensions of the proposed antenna are:

• Semi major axis a = 15mm

• Semi minor axis b = 10mm

• Position of the square slot= (0, 5)

• Square slot area = 3mm×3mm

Use of pin short

To obtain the desired bandwidth a pin short at point (2, -2) has been used. The position of pin is in the fourth quadrant while the feed is used in third quadrant at same distance from origin. The pin changes the distribution of current so improves the bandwidth.

Return loss and bandwidth

The return loss with feed only was obtained -19.55dBi which have been improved to -38.84dBi and previously the bandwidth was 2.93% and after modification in geometry improved bandwidth is 21.048%.

Figure 6 (a) and (b) simulated return loss verses frequency graph for conventional elliptical

patch and proposed geometry

Smith chart

The corresponding smith chart of before modification and after modification in elliptical shape patch is shown in figure below. The figure shows that input impedance of is (55.12- j9.42) for simple feed geometry and (49.68- j1.10) for modified geometry.

Figure 7 (a) and (b) smith chart of conventional elliptical patch and geometry

Radiation Pattern

Figure 3.12 (a) and (b) 2D-Radiation pattern of elliptical patch without cut and with cut

Table 1 shows the comparison of results between modified and unmodified geometry

S.

No. Characteristic

Elliptical patch with only feed

Elliptical patch with a slot of

square shape

Elliptical patch with square slot and a pin shot

1. Resonant

frequency(GHz) 4.97 4.99 7.25 2. Return loss(dB) -19.55 -19.47 -38.84 3. Gain (dBi) 1.56 1.63 0.25 4. Bandwidth 2.93 2.968 21.04

5. Antenna

Efficiency (%) 21.52 22.27 16.43

6. Radiation

Efficiency (%) 22.53 23.03 16.82

Conclusions

used. For the same dimensions conventional patch had bandwidth 2.93% and proposed design had bandwidth of 21.04%. The proposed antenna can be used a broadband antenna.

References

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